The present invention relates to a device for selectively and/or partially preventing one or more modes of actuating manual control members equipping an apparatus.
It applies advantageously, but not exclusively, to apparatus of the overload relay type with manual and automatic reset generally called "manual-automataic reset thermal relays".
It will be recalled in this connection that a thermal relay is a protective apparatus associated with a contactor. Its purpose is to monitor the current flowing in the load (for example of a motor ), controlled by the contactor and to cause opening of this latter should an overload occur, that is to say for a current which may for example have a value between 1.05 and 1.2 times the nominal current of the load whose value is given by the constructor.
This relay generally includes thermally deformable bimetal elements heated by the current which flows through the load. From a certain threshold corresponding to an overload, these elements actuate a tripping device which controls the opening of a contactor.
After tripping, for bringing the load back into service, resetting can be achieved manually and/or automatically depending on whether it is a manual reset relay or a manual-automatic reset relay.
Usually, this latter type of relay has on one of the faces of the case, on the front face or on the upper face:
an adjustment knob for adjusting the protective device to the nominal current of the load controlled;
a knob for stopping the relay which acts on an opening contact; and
a double acting knob, movable in rotation and in axial translation which has two angular positions for selecting the manual reset mode and the automatic reset mode and two axial positions, namely a normal rest position and a pushed-in position (with possible return under the effect of a spring) corresponding to resettng.
It proves in this type of apparatus, if sufficient precautions are not taken and if, during manual resetting, an action is performed both pushing and rotating the double acting knob, the initial choice of the reset mode can be accidently changed.
The invention has then more particularly as aim to overcome this type of disadvantage.